Wednesday, 17 June 2009

The colour of anemone

For a scuba diver, one of the best underwater sights is a rock face covered in brilliantly coloured jewel anemones (Corynactis viridis). They exist in many colours, and often vivid contrasting colours are found side by side. There are also subdued, semi-transparent variants.

Most species of wild animals have evolved to just one or a narrow range of colours, while flowers can have a range of vivid colours, presumably to attract a variety of insects. As far as I know, the anemones aren't trying to attract their prey - it just arrives on the current. So why are they so vivid and so varied?

I had a cold water marine tank with local prawns and beadlet anemones, among other creatures, in it. I often noticed a prawn with its antenna caught by an anemone. You'd think the antenna would be quite a sensitive part of the prawn, but the prawn didn't pay any attention and would stay put for several minutes until something called it away, and it tugged itself free.

There wouldn't be a lot of evolutionary advantage in an anemone stinging, would there? Paralysing and harpooning, yes, but not stinging.

Well anemones do indeed sting, but the stinging cells (blastocysts) in different species (be they jellyfish or anemone) vary in the depth of tissue they can penetrate. Human skin (even on our very sensitive fingers) is an effective barrier to many types of anemone so I would imagine that the firm covering on a prawn's antenna would be also?

Why should an anemone evolve a sting? If anything, you'd think a sting would just alert its prey to danger. Better to evolve anaesthetic and something to cause paralysis so the prey can be pulled in, surely?

Reminds me of my favourite pick-up line: do you think this cloth smells of chloroform?

Sea Anemones are single - often colony forming,mobile polyps(though they hardly move once found a suitable place) with cylindrical body which attach to the rock or sand by an adhesive disk,at the other end there is the mouth surrounded by tentacles.These tentacles bear poisonous (sometimes with neurotoxins)stings which they use to catch prey.

They have got there name from the flower of same name due to their bright appearece,which is used both to lure the prey and give out a signal that they are too toxic to mess with.Its an evolutionary adaptation to ward off enemies at the least cost by advertising their colour.

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